The present invention relates to a method and an apparatus for handling semiconductor single crystal wafers, or more particularly to a method and an apparatus for holding and transporting polished wafers whereby they are brought to be stored in wafer cassette, etc. without being damaged or polluted.
At the polishing stage in a typical conventional semiconductor manufacturing process, a semiconductor single crystal wafer W has one of its faces polished by means of a single (or individual) wafer polishing apparatus, which polishes wafers one after another, as shown in FIG. 5. Incidentally, FIG. 5 is a top plan view of a single wafer polishing apparatus wherein a plurality of wafers W stored in a cassette 30 at a load sector A are automatically transported one by one to a polish sector B; then, the wafers W polished at the polish sector B are automatically transported one after another to an unload sector C and stored in a cassette 40 in the same order as they were polished.
At the polish sector B, as shown in FIG. 6, a wafer W is sucked firmly to stick to the lower face of a wafer holder plate 51, which is supported at the lower end of a rotary shaft 50. The plate 51 is turned about the shaft 50 together with the wafer W and the wafer W is thus pressed with a predetermined force onto a polishing cloth 53 pasted over a turn table 52, which is also kept turning at a predetermined rotational speed, as indicated by the circular arrow in FIG. 6. An abrasive powder 55 is supplied over the polishing cloth 53 from a nozzle 54 and the lower face of the wafer W is polished with the polishing cloth 53 supplemented by the abrasive powder 55 until the lower face of the wafer W gains a specular gloss.
In recent years, the demand for higher integration of the semiconductor devices has necessitated the wafers to have surfaces of increased flatness, cleanness, and crystallographical regularity.
Thus, the wafer handling operation (such as holding the polished wafers, transporting them to the unload sector C and storing them in the wafer cassette 40) must be conducted with a special care and tenderness so that the once glossed surfaces of the wafers W are not damaged or polluted thereafter.
FIG. 7 shows a manner of a water-borne transportation method which has been conventionally adopted in the wafer handling operation. In this method water is spurted or ejected from nozzles 61, which are made through a transportation table 60, in a manner such that a laminar water stream 62 flowing in the direction toward a cassette 40 is formed over the surface of the transportation table 60. A wafer W already polished is dropped from the wafer holder plate 51 with the polished face facing downward over the water stream 62 whereupon the wafer W is water-borne like a fallen leaf on a river surface and carried into the cassette 40 one by one while the water falls into the space between the transportation table 60 and the wafer cassette 40.